Project Summary/Abstract Periodontal disease is a complex inflammatory disease resulting not from a single organism, but rather a dysbiotic community of oral microbes working together to promote disease. Inflammation associated with disease is initiated by members of the oral biofilm, but the host response to the microorganisms, including inflammatory reactions by macrophages, is primarily responsible for disease progression. Streptococcus gordonii is a normally innocuous inhabitant of the oral cavity but is also involved in the progression of periodontal disease, partially by promoting colonization of more pathogenic bacteria. Although both S. gordonii and macrophages are individually important in periodontal disease progression, little is known about their interactions. We have found a novel, yet counterintuitive, relationship between macrophages and S. gordonii where the bacterium is better able to survive within, and promote enhanced cytokine release from macrophages with an inflammatory phenotype similar to those present during disease. However, there remains a gap in the mechanistic understanding of oral streptococcus-immune interactions with macrophages, and how changes in this interaction may contribute to the ability of S. gordonii and/or macrophages to contribute to disease. The overall objective of this project is to examine the mechanisms behind the observed immune consequences of S. gordonii interaction with inflammatory macrophages. The central hypothesis is that S. gordonii perpetuates inflammation by actively damaging macrophage phagosomes and activating the cytoplasmic inflammasome, a subsequent pro-inflammatory response. To investigate this hypothesis this project aims to (1) define the macrophage cellular mechanisms manipulated by S. gordonii to promote inflammatory response by macrophages and (2) examine the acute responses of in vivo inflammatory macrophages responding to S. gordonii. To achieve these aims a wide variety of techniques, from classical cell biology and biochemical techniques to advanced microscopy, flow cytometry and animal models will be used. Completion of this project will be a valuable step in understanding the dynamic interplay of commensals and the innate immune system and how the two play a role in disease progression. It will also provide the investigator with diverse mentoring, scientific and professional training, as further outlined in the proposal, to allow a successful transition to the next stage of independently leading a successful research team.